Hi Georgina
I found an interesting article on the Kings College London that summarises research that was published in the Lancet last year. It refers to the use of antidepressants setraline and mirtazapine and their effect on dementia. You might like to read it here.
http://www.kcl.ac.uk/ioppn/news/rec...mentiapatientscouldprovemoreharmthangood.aspx
Although I looked after my mother at home because she would never have liked to have ended up in a CH, I did occasionally have to put her in one for a few days in order to get some respite. I noticed a considerable change in her mood when she was in the CH. She became withdrawn and seemed totally lost. From what I now know in having done a course on Dementia, this withdrawal results from depression. It kind of makes sense to me now because once she came home, she brightened up considerably.
Although each person and case is so different, there may be some issues with the CH that are affecting your dad for example. Something my be upsetting him. He may be feeling isolated, worried about his condition or that he is unable to do certain things. It might be worth looking into it in more detail.
In the later stages of her dementia, my mother was prescribed mirtazapine because of her agitation. However, it seemed to create more insomnia and hence wasn't of any benefit.